Thermoplastic resins are plastics which are softened and plasticized by heating and are hardened by cooling. Thermoplastic resins are divided into: common plastics such as polyethylene, polypropylene, acrylic, styrene, and vinyl resins; and engineering plastics such as polycarbonate, polyphenylene ether, polyamide, polyester, and polyimide resins.
Thermoplastic resins are widely utilized in numerous applications, including various household supplies, office automation equipment, and electric and electrical appliances, owing to their superior processability and formability. There has been a continuous attempt to use a thermoplastic resin as a high value-added material by imparting specific properties as well as superior processability and formability to the thermoplastic resin, according to the kind and properties of products in which the thermoplastic resin is used. In particular, there have been various attempts to impart electrical conductivity to a thermoplastic resin and utilize the electrically conductive thermoplastic resin in the manufacture of automobiles, electric apparatuses, electronic assemblies, and electrical cables with electromagnetic wave shielding performance.
Electrically conductive thermoplastic resin is conventionally prepared from an electrically conductive thermoplastic resin composition obtained by mixing a thermoplastic resin with a conductive additive, such as a carbon black, a carbon fiber, a metallic powder, a metal-coated inorganic powder or a metallic fiber. To ensure a desired level of electrical conductivity of the electrically conductive thermoplastic resin, the conductive additive must be used in significantly large amounts. However, the use of the conductive additive in significantly large amounts can deteriorate impact resistance, which is one of the basic mechanical properties of the thermoplastic resin.
In addition, there have also been efforts to impart superior electrical conductivity to a thermoplastic resin using carbon nanotubes as a conductive additive.
However, when an electrically conductive thermoplastic resin is prepared by mixing a thermoplastic resin with carbon nanotubes and injecting the composite resin mixture using injection molding equipment, the carbon nanotubes may aggregate or unexpectedly orient due to shearing stress occurring during the injection. As a result, the carbon nanotubes contained in the electrically conductive thermoplastic resin are not well dispersed, thus making it difficult to ensure sufficient electrical conductivity of the thermoplastic resin.